An interface circuit for charging a capacitor used in a voltage-raising circuit is described in European Patent Application n.degree.0 342 581. In the transient regime, when the input signal of the interface circuit changes from the high level to the low level for example, the first and the second transistors of this second branch are both on for a short instant. This brief short-circuit creates a current spike which is higher as the dimensions of the two transistors is made larger.